Question: Which of these numbers is composite? ${5,\ 31,\ 47,\ 61,\ 77}$
A composite number is a number that has more than two factors (including 1 and itself). 5, 31, 47, and 61 each have only two factors. The factors of 77 are 1, 7, 11, and 77. Thus, 77 is the composite number.